1. Field of the Invention
The present invention relates to a process and apparatus for the separation of a mixture comprising more than one organic substance, or a mixture comprising one or more than one organic substance and water, using a supercritical fluid.
2. Description of the Related Art
A separation process using a supercritical fluid is used in various industries, and this technique has aroused interest from the point of view of saving energy and resources. Compared with the usual extraction process and distillation, this technique has the following advantages: improved extraction efficiency because of higher selectivity of the supercritical fluid, lower energy costs because the change of phase for separation and recovery of an extract and extractant become unnecessary, treatment of a heat-susceptible substance without degradation due to a relatively low working temperature, and easy elimination of residual solvent in product, and so on. Therefore much research is underway in a wide range of industrial fields, including the food processing and pharmaceutical industries. Typical applications of this technique are the extraction and separation of hydrocarbons, the elimination of caffeine from coffee, the extraction of a hop extract in beer production, the extraction of natural flavors, the elimination of nicotine from tobacco, and the isolation of alcohol from an aqueous alcohol solution.
As described above, although the supercritical fluid extraction process has many advantages, the separation ability thereof is limited in cases wherein components to be separated have similar boiling points, or wherein components to be separated form an azeotropic mixture. For example, Japanese Unexamined Patent Publication No. 59-141528 discloses a process for the concentration of an ethanol aqueous solution under a three-phase condition of gas / light liquid / heavy liquid. Murakami et al., in "Separation of Ethanol Aqueous Solution by Supercritical Gas" (18th Annual Meeting, The Society of Chemical Engineering, Japan AS 109, 1984), reported the use of a separation process using a supercritical fluid. Nevertheless, the supercritical fluid extraction process cannot increase the ethanol concentration to a rate higher than 90% by weight, and this concentration limit is lower than that obtained by distillation, which can increase the ethanol concentration to a rate of up to 95.6% by weight.